DC-DC converters which generate an output voltage that is stabilized by an input voltage are known. A variety of systems have been proposed as means for stabilizing the output voltage of a DC-DC converter. For example, Patent Document 1 mentions a switching DC-DC converter which uses a PWM (pulse width modulation) system. With the PWM system, the output voltage can be stabilized by fixing the switching frequency and adjusting the ON pulse width. There are also switching DC-DC converters which employ a comparator system. With a comparator system, the output voltage can be stabilized by using the comparator to fix the ON pulse width and adjust the OFF pulse width (that is, the switching frequency).
This DC-DC converter is sometimes used as the power source of a PU (Processor Unit) or the like. When the PU moves from a standby state to a processing state, the current consumption increases suddenly. When the output voltage suddenly drops as a result of a sudden increase in the load current, the comparator-system DC-DC converter immediately outputs an ON pulse and, therefore, in comparison with a PWM system which is incapable of outputting a pulse in a predetermined OFF pulse period, the output voltage stabilizes rapidly. Thus, in comparison with a PWM system, a comparator-system DC-DC converter may have the characteristic of a favorable response characteristic with respect to a sudden increase in the load current.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2000-287439